doc,lib,src,test: strip executable bits off files

Remove the executable bits of the file modes of some files that
accidentally received it.

PR-URL: #15132
Reviewed-By: Timothy Gu <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: addaleax